The newer engines place increased demands on the lubricants to be employed. In the past a number of different additives have been added to lubricating oils to improve such properties as viscosity index and dispersancy. Significant reductions in cost can be made by employing a single additive that improves a number of lubricant properties. However, in attempting to improve more than a single lubricant property, care must be taken in not causing the deterioration of other properties. For example, while the modified EPDM polymer additive disclosed in U.S. Pat. No. 3,864,268 may improve both dispersancy and viscosity characteristics over a narrow range, by employing an oxidation step to attach polar groups to the polymer backbone the patentees have reduced lubricant stability by introducing sites for oxidative attack. Likewise, the lubricant additive disclosed in U.S. Pat. No. 3,842,010, lacks a certain amount of oxidative stability due to the employment of an epoxidation step to attach polyamine groups to the polymer backbone.
A new lubricant additive having both dispersant and viscosity-index improving properties as well as good oxidative stability has now been found.